Had a surface temp thermometer (the one with a laser that painters use to see if a surface is too hot or cold to paint... benefits of having a dad as a painting contractor). I didn't count it as being 155 until I took the keg out of the water, flipped it over, and took a reading of the surface of the keg that was NOT submerged in water (since metal is such a good conductor of heat). I held the actually water temp at about 160 for roughly 2 hours.